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Response of permafrost landscapes of Central Yakutia to current changes of climate, and anthropogenic impacts
Geography and Natural Resources 30 (2009) 146–150
Response of permafrost landscapes of Central Yakutia to current changes of climate, and anthropogenic impacts A. N. Fedorov * and P. Ya. Konstantinov Permafrost Institute SB RAS, Yakutsk Received 1 September 2008
Abstract We discuss the state of permafrost landscapes of Central Yakutia under the influence of current changes of climate and anthropogenic impacts. This study uses the data from the monitoring stations operated by the Permafrost Institute SB RAS, and from the Yakutsk and Pokrovsk meteorological stations. It is found that there is a rather good correlation between the data from the monitoring stations and from the Pokrovsk meteorological station. The last decade saw a considerable rise in temperatures of earth materials. The most sensitive to climate change are the disturbed landscapes, primarily treeless landscapes such as anthropogenic complexes, and burned-out forests. Keywords: permafrost landscape, climate change, temperature of earth materials, cryogenic processes, thermokarst.
Direct monitoring observations of the temperature regime of earth materials on special-purpose study sites operated by the P. I. Melnikov Permafrost institute SB RAS, which are located in Central Yakutia, have been carried on since 1980 till the present; however, for understanding of the temperature variation patterns of earth materials, it is necessary to use a longer series of data from meteorological stations ;1–5=. In the case of the meteorological stations in Central Yakutia there is largely a pronounced positive trend of temperature variation of earth materials. The objective of this paper is to assess the state of permafrost landscapes and temperature conditions of earth materials in Central Yakutia within the context of current changes of climate. Materials and methods of investigation In central Yakutia, continuous measurements of temperatures of earth materials have been made since 1931 at meteorological stations Yakutsk and Pokrovsk. Such observations at a depth of 1.6 and 3.2 m provide a means of assessing monthly average as well as year-to-year temperature variations of soils and earth materials. As a result of data analysis, we decided to choose the temperature series (st. Pokrovsk) * Corresponding author. E-mail addresses: [email protected] (A. N. Fedorov), [email protected] (P. Ya. Konstantinov)
as the most representative model for Central Yakutia. The study site at st. Pokrovsk was relocated in 1941, without affecting the temperature indices of earth materials, because the landscape and earth materials conditions of the old and new sites were virtually identical. The site at st. Yakutsk was moved in 1964, and there was a considerable difference between the old and new sites and, hence, the values of temperature series experienced changes. Note that for the period 1965-1988 the correlation coefficients for yearly average temperatures of earth materials at a depth of 1.6 and 3.2 m at stations Pokrovsk and Yakutsk were 0.85 and 0.88, respectively, with р = 0.05; furthermore, the conditions of measurement were not disturbed by the relocations and the influence of the anthropogenic factor. To assess the influence of climate change on permafrost landscapes we used the data obtained on monitoring sites Yukechi and Umaibyt, and at permanent stations Neleger and Spasskaya Pad, in Central Yakutia. These sites are used to measure temperatures of earth materials, depths of seasonal thawing, and moisture content of earth materials in the active layer as well as to monitor the dynamics of the microrelief and microlandscapes at the level of facies peaks ;6-11=. Temperature of earth materials at permanent stations Spasskaya Pad and Neleger shows a rather good correlation with the data from st. Pokrovsk. Thus, the correlation coefficient of monthly mean temperatures at a depth of 3.2 m from October 2000 to September 2005 was 0.89 (st. Pokrovsk – Spasskaya Pad) and 0.92 (st. Pokrovsk – Neleger).
Copyright © 2009 IG SB, Siberian Branch of RAS. Published by Elsevier B.V. All rights reserved 48 doi:10.1016/j.gnr.2009.06.010
A. N. Fedorov and P. Ya. Konstantinov / Geography and Natural Resources 30 (2009) 146–150
Note that the air temperature dynamics in Central Yakutia is relatively homogeneous. The correlation coefficient between individual meteorological stations here is 0.89-0.98 ;12=. Year-to-year temperature variations of earth materials For the analysis of the long-term temperature dynamics of earth materials we used a depth of 3.2 m, because under climatic conditions of Central Yakutia the earth materials at this depth are always in a perennially frozen state. Changes in soil temperature in the upper part of permafrost is a significant landscape-forming importance. Thus, a rise in temperature gives rise to an intensification of cryogenic processes, whereas its drop promotes stability of the upper horizons of permafrost. During 1931–2007, the yearly average soil temperature at a depth of 3.2 m (st. Pokrovsk) was –2.4 оС, with the standard deviation of the series being 0.5 оС. Furthermore, the maximum amplitude of yearly average values was 2.3 оС (tav min = –3.3 оС, and tav. max = –1 оС). The highest soil temperatures were observed in 2006–2007. During the period from 1931 to 2007 the yearly average soil temperature increased by 0.8 оС; the trend was 0.1 оС/10 years (Fig. 1). The time variation of yearly average soil temperatures has a cyclic progressive-increasing character (in the positive as well as negative phase). The cycle duration averages 9.6 years, and the maximum and minimum cycle lengths are 12 and 8 years, respectively. Relatively high soil temperatures were recorded in the mid-1930s the early 1940s, the late 1940 – early 1950s, the late 1950s – early 1960s, the late 1960s – early 1970s, the early – mid-1980s, the early 1990, the late 1990s – early 2000s, and in the mid-2000s. Of them, two positive phases (the early 1940s, and the late 1950s – early 1960s) are less clearly pronounced when compared with the others.
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The time interval in the mid-1990s drops out of the general series, when there occurred a decrease in temperature as well as a relatively slight increase at the end of the 1990s – beginning of 2000s. Noteworthy are also the periods of maximum soil temperature increases corresponding to the early – mid-1980s, and to the beginning of the 1990s. In the time interval under consideration, periods with maximum temperatures were longer, and periods with minimum temperatures were short. The anomalously warm 20052007 were due to abundant atmospheric precipitation in the summer time, and to the thick snow cover. Before the 1980s, the temperature series can be characterized as a relatively stable series, with an alternation of positive and negative phases. Analysis of the series of yearly average air temperature variation lends credence to the fact that it started to increase dramatically in the late 1980s, and the temperature series changed its usual behavior characteristic for this time period (Fig. 2). For instance, the yearly average air temperature at st. Yakutsk for the period from 1988 to 2007 increased to –8.5оС against the normal temperature of –10.2 оС ;13=. Consequently, the soil temperature rise in the early – mid-1980s was not associated with the abrupt jump of air temperature. At the same time, before the mid-1950s air temperatures at st. Pokrovsk were higher than at Yakutsk; from the mid1950s till the mid-1970s it was about the same, and since the mid-1970s till the present it was lower than at st. Pokrovsk, which is most likely due to a change of natural circulation processes rather than to the anthropogenic factor ;12=.
Fig. 2. Variability of running annual average five-year air temperatures at meteorological stations Yakutsk (1) and Pokrovsk (2).
Characteristics of the response of cryogenic landscapes to impacts under current climatic conditions
Fig. 1. Long-term temperature variation of earth materials at the Pokrovsk meteorological station at a depth of 3.2 m. 1 – annual data; 2 – five-year running data; 3 – trend.
Over a period of years, within the research programs of the Permafrost Institute SB RAS, we have doing research into the dynamics of permafrost and cryogenic landscapes evolving as a consequence of various technogenic disturbances ;78, 10, 14-17=. The study of thermokarst is a major area of this
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A. N. Fedorov and P. Ya. Konstantinov / Geography and Natural Resources 30 (2009) 146–150
research and is being underway on special-purpose research sites near the city of Yakutsk: Yukechi, Neleger, Spasskaya Pad, and Umaibyt. The location of the research sites is characterized by a widespread occurrence of subterranean ice whose presence in the lithogenic base is the main cause for the development of thermokarst. The presence of wedge ice is quite well indicated by the occurrence of cemetery mounds (“baidzherakhs”) on the slopes of the alasses and “bylars” (subsidence-polygonal forms) in disturbed areas. Such landscapes on the territory of Yakutia occupy merely about 10% of the total area. Their most widespread occurrence corresponds to the densely populated areas: the Lena-Amga interfluve, and the Vilyui and Kolyma river basins. Thermokarst does not always develop intensely in areas containing large amounts of ice. As is known, at the time of climate warming during the Pleistocene and Holocene, about 80-85% of the territory of Central Yakutia remained unchanged. Only 10-20% of the territory was affected by thermokarst and transformed to alas landscapes afterwards ;18=. The factors and mechanisms of stability of such landscapes are as yet poorly understood. The climatic factors has a special role in the development of thermokarst. Since the 1990s, in Central Yakutia there has been taking place a universal temperature rise accompanied by an intense development of thermokarst in landscapes disturbed previously by humans. The ground ice in such areas occurs near the daytime surface, at a depth of about 2-2.2 m on the average. A long-lasting presence of landscape in a man-made state affects its characteristics – the active layer dries out to a large extent, and its thawing does not use the amount of heat which is necessary for humidified earth materials in forest complexes. Therefore, in the warmest years the depth of seasonal thawing almost always reaches the upper boundary of the wedge ice thereby causing its melting and ground subsidence. Original data on the development of thermokarst landforms were obtained on the Kerdyugen plot near the settlement of Tabaga in the surroundings of the city of Yakutsk [19]. An intense development of incipient thermokarst landforms was studied in an abandoned ploughed field. While thermokarst affected only small local areas of the ploughed field in 1987, thermokarst sinkholes occupied nearly a half of the territory in 1993, and in more recent years the entire territory (about 100 ha) was affected by thermokarst. Thermokarst was studied in greater detail on the Yukechi plot situated 50 km to the east of Yakutsk, on the right bank of the Lena river. This area is characterized by an extensive occurrence of thermokarst landforms. Current warming caused an extensive intensification of thermokarst in pre-existing thermokarst depressions. During 1992-2007, the rate of subsidence averaged 5-10 m per year in the middle parts of young waterlogged thermokarst depressions 2-2.5 m in depth (Fig. 3). Interesting data were obtained in areas which were not affected previously by thermokarst processes. Such areas are
Fig. 3. Sinkholes on site 2, Yukechi (young thermokarst depression). С – control point, undisturbed terrain between the alasses; D – incipient thermal sinkhole; 1-3 – observing centers inside an areal sinkhole.
represented by flat-plain forestless, well drained terrains between the alasses without any visible manifestations of the thermokarst process, or sinkholes along the wedge ice pattern. Such areas, however, started also to show in recent years ground subsidence events, which is due primarily to the rise in air temperature. Forestless landscapes with a dried-out active layer are the most sensitive to climate warming and are the most hazardous as regards subsequent disturbances. Analysis of the data obtained showed that sinkholes are produced in the “pulsed mode”, or following a certain rhythm. Thus, considerable thermokarst sinkholes occurred in 1995-1996, then in 2000-2001, and subsequently in 2004 and 2006-2007. Furthermore, they are not so much associated with the rise in air and earth materials temperature as with the increase of the amount of atmospheric precipitation. At permanent station Neleger we studied the present-day response of disturbed areas on permafrost containing large amounts of ice (Fig. 4). It was found that the cryogenic processes are the most active during the first 5-6 years after a disturbance of the surface conditions, followed by a stabilization of these processes thus creating favorable conditions for the recovery of permafrost landscapes. If this is time-coincident with the regeneration of the forest cover, then the disturbed area is virtually beyond the zone of ecological risk. Thus, after clear felling operations in 1996 the Kys-Alas plot (permanent station Neleger), composed by deposits with high ice content, started to develop intense thermokarst events with ground subsidences to a depth of 10-15 cm which continued till 2001. After that, during the period before 2004, there occurred ground heaving due to freezing of the thawed out layer, with its elevations exceeding even the original values. Subsequently (2004-2007), a relatively stable situation was observed (see Fig. 4). The excessive moisture content in earth materials of the active layer in the first years after clear felling plus an intermittent enhanced cooling of earth materials at the beginning of the winter, caused by the deficit of snow in the winter seasons 2001/2002, 2002/2003 and
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Fig. 4. Dynamics of variation in relative elevation for different periods of time.
2003/2004, were responsible for the discontinuance of the permafrost thawing process. That affected the formation of the ice-containing layer at a depth of 110-180 cm which has a protective role. In recent years the depth of thawing in this area did not exceed 110 cm. Also, the relative elevations of the surface increased by 10-15 cm, on the average (see Fig. 4). It is likely that a stabilization of the permafrost situation promotes the recovery and optimization of cryogenic landscapes which were disturbed previously. Conclusion The ongoing changes in air and earth materials temperature are reflected in the modification of permafrost landscapes of Central Yakutia. The most sensitive under these conditions are the disturbed landscapes, primarily where the forest cover was destroyed as a result of economic utilization of the territory (ploughed fields, and cutting). Such permafrost landscapes are the most vulnerable and dependent on fluctuations of meteorological conditions at the period of current climate warming. At the same time, the results of our investigations showed that permafrost landscapes have some potential for self-stabilization; therefore, the degradation cryogenic processes still are taking place on a limited territory.
This work was done with financial support under the SB RAS project “Investigation of the state and tendencies of development of cryogenic landscapes in view of climate change, the changing hydrogeological conditions, and anthropogenic impacts” (7.10.2.5). References 1. Skryabin P. N., Varlamov S. P. and Skachkov Yu. B. Year-toYear Variability of the Thermal Regime of Earth Materials in the Area of Yakutsk. Novosibirsk: Izd-vo SO RAN, 1998, 144 p. 2. Varlamov S. P., Skachkov Yu. B. and Skryabin P. N. The Temperature Regime of Permafrost Landscapes of Central Yakutia. Yakutsk: Permafrost Institute SB RAS Publisher, 2002, 218 p. 3. Pavlov A.V. Permafrost-climatic changes in northern Russia: observations, forecasts. Izv. RAN. Ser. geogr., 2003, No. 6, pp. 39-50. 4. Vasiliev I. S. and Torgovkin Ya. I. Influence of climate on temperature and thickness of thawing soils and earth materials. In: Influence of Climate on Permafrost Landscapes of Central Yakutia. Yakutsk: Permafrost institute SB RAS Publisher, 1996, pp. 37-45. 5. Romanovsky V. E., Sazonova T. S., Balobaev V. T. et al. Past and recent in air and permafrost temperatures in earstern Siberia. Global and Planetary Change, 2007, 56(3–4), pp. 399– 413.
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6. Konstantinov P. Ya., Argunov R. N., Gerasimov E. Yu., and Ugarov I. S. On the connection of the depth of seasonal thawing with year-to-year average annual temperature variability of earth materials. Kriosfera Zemli, 2006, v. 10, No. 3, pp. 15-22. 7. Fedorov A. N. Effects of recent climate change on permafrost landscapes in Central Sakha. Polar Geography, 1996, 20, 2, pp. 99-108. 8. Fedorov A. N., Konstantinov P. Ya., Vassiliev I. S. et al. Observations of permafrost-landscape dynamics related to anthropogenic disturbances, Yukechi study site, Central Yakutia. PERMAFROST. Seventh International Conference. June 2327, 1998. Proceedings. Yellowknife, Canada, 1998, pp. 259263. 9. Konstantinov P. Y., Rusakov V. G. and Fukuda M. Thermal regime of the upper permafrost layers in taiga landscapes, Yakutsk Area, 1996-2000. Proceedings of the Ninth Symposium on the Joint Siberian Permafrost Studies Between Japan and Russia in January 23–24 2000. Sapporo, 2001, pp. 204-209. 10. Fedorov A. N. and Konstantinov P .Y. Observations of surface dynamics with thermokarst initiation, Yukechi site, Central Yakutia. Permafrost: Proceedings of the 8th International Conference on Permafrost, 21-25 July 2003, Zurich, Switzerland. Vol. 1. A. A. BALKEMA Publishers, 2003, pp. 239-243. 11. Fedorov A. N., Gavriliev P. P. and Konstantinov P. Ya. The study of the dynamics of permafrost landscapes on the territory of the “Spasskaya Pad” permanent station. Nauka i obrazovaniye, 2003, No. 3, pp. 62-65.
12. Skachkov Yu. B. Current climate changes in central Yakutia. In: Climate and Permafrost: Integral Research in Yakutia. Yakutsk: Permafrost institute SB RAS Publisher, 2000, pp. 55-63. 13. Scientific Application-Oriented Handbook on the USSR Climate, issue 24, Yakut ASSR. Leningrad: Gidrometeoizdat, 1989, 608 p. 14. Bosikov N. P. Humidification variability of Central Yakutia and dynamics of thermokarst processes. In: Problems in Geocryology. Yakutsk: Izd-vo SO RAN, 1998, pp. 123-127. 15. Bosikov N. P. Technogenic karst-induced destruction of landscapes between the alasses on the Lena-Amga interfluve. Kriosfera Zemli, 2004, v. 8, No. 4, pp. 12-14. 16. Gavriliev P. P., Ugarov I. S. and Yefremov P. V. Permafrostecological monitoring of agricultural lands in Central Yakutia. Kriosfera Zemli, 1999, No. 3, pp. 92-99. 17. Gavriliev P. P., Ugarov I. S. and Yefremov P. V. Cryogenic processes and variation in rock stability of the ice complex in Central Yakutia under current climate change and disturbances of surface. Nauka i obrazovaniye, 2005, No. 4 (40), pp. 84-87. 18. Bosikov N. P. Formation of alasses in Central Yakutia. In: Geocryological Conditions in the Mountains and on the Plains of Asia. Yakutsk: Permafrost Institute SB RAS Publisher, 1978, pp. 113-118. 19. Gavriliev P. P., Ugarov I. S. and Yefremov P. V. The Permafrost-Ecological Properties of Taiga Agrolandscapes of Central Yakutia. Yakutsk: Permafrost Institute SB RAS Publisher, 2001, 195 p.
Response of permafrost landscapes of Central Yakutia to current changes of climate, and anthropogenic impacts A. N. Fedorov * and P. Ya. Konstantinov Permafrost Institute SB RAS, Yakutsk Received 1 September 2008
Abstract We discuss the state of permafrost landscapes of Central Yakutia under the influence of current changes of climate and anthropogenic impacts. This study uses the data from the monitoring stations operated by the Permafrost Institute SB RAS, and from the Yakutsk and Pokrovsk meteorological stations. It is found that there is a rather good correlation between the data from the monitoring stations and from the Pokrovsk meteorological station. The last decade saw a considerable rise in temperatures of earth materials. The most sensitive to climate change are the disturbed landscapes, primarily treeless landscapes such as anthropogenic complexes, and burned-out forests. Keywords: permafrost landscape, climate change, temperature of earth materials, cryogenic processes, thermokarst.
Direct monitoring observations of the temperature regime of earth materials on special-purpose study sites operated by the P. I. Melnikov Permafrost institute SB RAS, which are located in Central Yakutia, have been carried on since 1980 till the present; however, for understanding of the temperature variation patterns of earth materials, it is necessary to use a longer series of data from meteorological stations ;1–5=. In the case of the meteorological stations in Central Yakutia there is largely a pronounced positive trend of temperature variation of earth materials. The objective of this paper is to assess the state of permafrost landscapes and temperature conditions of earth materials in Central Yakutia within the context of current changes of climate. Materials and methods of investigation In central Yakutia, continuous measurements of temperatures of earth materials have been made since 1931 at meteorological stations Yakutsk and Pokrovsk. Such observations at a depth of 1.6 and 3.2 m provide a means of assessing monthly average as well as year-to-year temperature variations of soils and earth materials. As a result of data analysis, we decided to choose the temperature series (st. Pokrovsk) * Corresponding author. E-mail addresses: [email protected] (A. N. Fedorov), [email protected] (P. Ya. Konstantinov)
as the most representative model for Central Yakutia. The study site at st. Pokrovsk was relocated in 1941, without affecting the temperature indices of earth materials, because the landscape and earth materials conditions of the old and new sites were virtually identical. The site at st. Yakutsk was moved in 1964, and there was a considerable difference between the old and new sites and, hence, the values of temperature series experienced changes. Note that for the period 1965-1988 the correlation coefficients for yearly average temperatures of earth materials at a depth of 1.6 and 3.2 m at stations Pokrovsk and Yakutsk were 0.85 and 0.88, respectively, with р = 0.05; furthermore, the conditions of measurement were not disturbed by the relocations and the influence of the anthropogenic factor. To assess the influence of climate change on permafrost landscapes we used the data obtained on monitoring sites Yukechi and Umaibyt, and at permanent stations Neleger and Spasskaya Pad, in Central Yakutia. These sites are used to measure temperatures of earth materials, depths of seasonal thawing, and moisture content of earth materials in the active layer as well as to monitor the dynamics of the microrelief and microlandscapes at the level of facies peaks ;6-11=. Temperature of earth materials at permanent stations Spasskaya Pad and Neleger shows a rather good correlation with the data from st. Pokrovsk. Thus, the correlation coefficient of monthly mean temperatures at a depth of 3.2 m from October 2000 to September 2005 was 0.89 (st. Pokrovsk – Spasskaya Pad) and 0.92 (st. Pokrovsk – Neleger).
Copyright © 2009 IG SB, Siberian Branch of RAS. Published by Elsevier B.V. All rights reserved 48 doi:10.1016/j.gnr.2009.06.010
A. N. Fedorov and P. Ya. Konstantinov / Geography and Natural Resources 30 (2009) 146–150
Note that the air temperature dynamics in Central Yakutia is relatively homogeneous. The correlation coefficient between individual meteorological stations here is 0.89-0.98 ;12=. Year-to-year temperature variations of earth materials For the analysis of the long-term temperature dynamics of earth materials we used a depth of 3.2 m, because under climatic conditions of Central Yakutia the earth materials at this depth are always in a perennially frozen state. Changes in soil temperature in the upper part of permafrost is a significant landscape-forming importance. Thus, a rise in temperature gives rise to an intensification of cryogenic processes, whereas its drop promotes stability of the upper horizons of permafrost. During 1931–2007, the yearly average soil temperature at a depth of 3.2 m (st. Pokrovsk) was –2.4 оС, with the standard deviation of the series being 0.5 оС. Furthermore, the maximum amplitude of yearly average values was 2.3 оС (tav min = –3.3 оС, and tav. max = –1 оС). The highest soil temperatures were observed in 2006–2007. During the period from 1931 to 2007 the yearly average soil temperature increased by 0.8 оС; the trend was 0.1 оС/10 years (Fig. 1). The time variation of yearly average soil temperatures has a cyclic progressive-increasing character (in the positive as well as negative phase). The cycle duration averages 9.6 years, and the maximum and minimum cycle lengths are 12 and 8 years, respectively. Relatively high soil temperatures were recorded in the mid-1930s the early 1940s, the late 1940 – early 1950s, the late 1950s – early 1960s, the late 1960s – early 1970s, the early – mid-1980s, the early 1990, the late 1990s – early 2000s, and in the mid-2000s. Of them, two positive phases (the early 1940s, and the late 1950s – early 1960s) are less clearly pronounced when compared with the others.
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The time interval in the mid-1990s drops out of the general series, when there occurred a decrease in temperature as well as a relatively slight increase at the end of the 1990s – beginning of 2000s. Noteworthy are also the periods of maximum soil temperature increases corresponding to the early – mid-1980s, and to the beginning of the 1990s. In the time interval under consideration, periods with maximum temperatures were longer, and periods with minimum temperatures were short. The anomalously warm 20052007 were due to abundant atmospheric precipitation in the summer time, and to the thick snow cover. Before the 1980s, the temperature series can be characterized as a relatively stable series, with an alternation of positive and negative phases. Analysis of the series of yearly average air temperature variation lends credence to the fact that it started to increase dramatically in the late 1980s, and the temperature series changed its usual behavior characteristic for this time period (Fig. 2). For instance, the yearly average air temperature at st. Yakutsk for the period from 1988 to 2007 increased to –8.5оС against the normal temperature of –10.2 оС ;13=. Consequently, the soil temperature rise in the early – mid-1980s was not associated with the abrupt jump of air temperature. At the same time, before the mid-1950s air temperatures at st. Pokrovsk were higher than at Yakutsk; from the mid1950s till the mid-1970s it was about the same, and since the mid-1970s till the present it was lower than at st. Pokrovsk, which is most likely due to a change of natural circulation processes rather than to the anthropogenic factor ;12=.
Fig. 2. Variability of running annual average five-year air temperatures at meteorological stations Yakutsk (1) and Pokrovsk (2).
Characteristics of the response of cryogenic landscapes to impacts under current climatic conditions
Fig. 1. Long-term temperature variation of earth materials at the Pokrovsk meteorological station at a depth of 3.2 m. 1 – annual data; 2 – five-year running data; 3 – trend.
Over a period of years, within the research programs of the Permafrost Institute SB RAS, we have doing research into the dynamics of permafrost and cryogenic landscapes evolving as a consequence of various technogenic disturbances ;78, 10, 14-17=. The study of thermokarst is a major area of this
148
A. N. Fedorov and P. Ya. Konstantinov / Geography and Natural Resources 30 (2009) 146–150
research and is being underway on special-purpose research sites near the city of Yakutsk: Yukechi, Neleger, Spasskaya Pad, and Umaibyt. The location of the research sites is characterized by a widespread occurrence of subterranean ice whose presence in the lithogenic base is the main cause for the development of thermokarst. The presence of wedge ice is quite well indicated by the occurrence of cemetery mounds (“baidzherakhs”) on the slopes of the alasses and “bylars” (subsidence-polygonal forms) in disturbed areas. Such landscapes on the territory of Yakutia occupy merely about 10% of the total area. Their most widespread occurrence corresponds to the densely populated areas: the Lena-Amga interfluve, and the Vilyui and Kolyma river basins. Thermokarst does not always develop intensely in areas containing large amounts of ice. As is known, at the time of climate warming during the Pleistocene and Holocene, about 80-85% of the territory of Central Yakutia remained unchanged. Only 10-20% of the territory was affected by thermokarst and transformed to alas landscapes afterwards ;18=. The factors and mechanisms of stability of such landscapes are as yet poorly understood. The climatic factors has a special role in the development of thermokarst. Since the 1990s, in Central Yakutia there has been taking place a universal temperature rise accompanied by an intense development of thermokarst in landscapes disturbed previously by humans. The ground ice in such areas occurs near the daytime surface, at a depth of about 2-2.2 m on the average. A long-lasting presence of landscape in a man-made state affects its characteristics – the active layer dries out to a large extent, and its thawing does not use the amount of heat which is necessary for humidified earth materials in forest complexes. Therefore, in the warmest years the depth of seasonal thawing almost always reaches the upper boundary of the wedge ice thereby causing its melting and ground subsidence. Original data on the development of thermokarst landforms were obtained on the Kerdyugen plot near the settlement of Tabaga in the surroundings of the city of Yakutsk [19]. An intense development of incipient thermokarst landforms was studied in an abandoned ploughed field. While thermokarst affected only small local areas of the ploughed field in 1987, thermokarst sinkholes occupied nearly a half of the territory in 1993, and in more recent years the entire territory (about 100 ha) was affected by thermokarst. Thermokarst was studied in greater detail on the Yukechi plot situated 50 km to the east of Yakutsk, on the right bank of the Lena river. This area is characterized by an extensive occurrence of thermokarst landforms. Current warming caused an extensive intensification of thermokarst in pre-existing thermokarst depressions. During 1992-2007, the rate of subsidence averaged 5-10 m per year in the middle parts of young waterlogged thermokarst depressions 2-2.5 m in depth (Fig. 3). Interesting data were obtained in areas which were not affected previously by thermokarst processes. Such areas are
Fig. 3. Sinkholes on site 2, Yukechi (young thermokarst depression). С – control point, undisturbed terrain between the alasses; D – incipient thermal sinkhole; 1-3 – observing centers inside an areal sinkhole.
represented by flat-plain forestless, well drained terrains between the alasses without any visible manifestations of the thermokarst process, or sinkholes along the wedge ice pattern. Such areas, however, started also to show in recent years ground subsidence events, which is due primarily to the rise in air temperature. Forestless landscapes with a dried-out active layer are the most sensitive to climate warming and are the most hazardous as regards subsequent disturbances. Analysis of the data obtained showed that sinkholes are produced in the “pulsed mode”, or following a certain rhythm. Thus, considerable thermokarst sinkholes occurred in 1995-1996, then in 2000-2001, and subsequently in 2004 and 2006-2007. Furthermore, they are not so much associated with the rise in air and earth materials temperature as with the increase of the amount of atmospheric precipitation. At permanent station Neleger we studied the present-day response of disturbed areas on permafrost containing large amounts of ice (Fig. 4). It was found that the cryogenic processes are the most active during the first 5-6 years after a disturbance of the surface conditions, followed by a stabilization of these processes thus creating favorable conditions for the recovery of permafrost landscapes. If this is time-coincident with the regeneration of the forest cover, then the disturbed area is virtually beyond the zone of ecological risk. Thus, after clear felling operations in 1996 the Kys-Alas plot (permanent station Neleger), composed by deposits with high ice content, started to develop intense thermokarst events with ground subsidences to a depth of 10-15 cm which continued till 2001. After that, during the period before 2004, there occurred ground heaving due to freezing of the thawed out layer, with its elevations exceeding even the original values. Subsequently (2004-2007), a relatively stable situation was observed (see Fig. 4). The excessive moisture content in earth materials of the active layer in the first years after clear felling plus an intermittent enhanced cooling of earth materials at the beginning of the winter, caused by the deficit of snow in the winter seasons 2001/2002, 2002/2003 and
A. N. Fedorov and P. Ya. Konstantinov / Geography and Natural Resources 30 (2009) 146–150
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Fig. 4. Dynamics of variation in relative elevation for different periods of time.
2003/2004, were responsible for the discontinuance of the permafrost thawing process. That affected the formation of the ice-containing layer at a depth of 110-180 cm which has a protective role. In recent years the depth of thawing in this area did not exceed 110 cm. Also, the relative elevations of the surface increased by 10-15 cm, on the average (see Fig. 4). It is likely that a stabilization of the permafrost situation promotes the recovery and optimization of cryogenic landscapes which were disturbed previously. Conclusion The ongoing changes in air and earth materials temperature are reflected in the modification of permafrost landscapes of Central Yakutia. The most sensitive under these conditions are the disturbed landscapes, primarily where the forest cover was destroyed as a result of economic utilization of the territory (ploughed fields, and cutting). Such permafrost landscapes are the most vulnerable and dependent on fluctuations of meteorological conditions at the period of current climate warming. At the same time, the results of our investigations showed that permafrost landscapes have some potential for self-stabilization; therefore, the degradation cryogenic processes still are taking place on a limited territory.
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